DFT study of the IR and Raman spectra of a fluorescent dendron built from cyclotriphosphazene core

Combined experimental and theoretical studies on molecular structure of the zero generation dendron, built from the hexafunctional cyclotriphosphazene core, with five OC₆H₄(CH₂)₂NHSO₂C₁₀H₆N(CH₃)₂ terminal groups and one oxybenzaldehyde group G₀ are reported. The Fourier transform Raman and IR spectra of G₀ have been recorded. Conformations of low energy isomers of G₀ have been studied at quantum-chemical level. The optimized geometry has been calculated by density functional (DFT) method at the PBE/TZ2P level of theory. The theoretical geometrical parameters, harmonic vibrational frequencies, IR intensities and Raman scattering activities are predicted in a good agreement with the experimental data. It was found that dendron molecule G₀ has a concave lens structure with planar OC₆H₄CHO fragments and slightly non-planar cyclotriphosphazene core. Relying on DFT calculations the bands of the core and terminal groups were assigned. The frequencies of ν(NH) bands in the IR spectrum reveal the presence of the H-bonds in the dendron.     

Continous gradient temperature Raman Spectroscopy identifies flexible sites in proline and alanine peptides

Continuous gradient temperature Raman spectroscopy (GTRS) applies the temperature gradients utilized in differential scanning calorimetry (DSC) to Raman spectroscopy, providing a straightforward technique to identify molecular rearrangements that occur near phase transitions. Herein we apply GTRS and DSC to the solid dipeptides Ala-Pro, Pro-Ala, and the mixture Ala-Pro/Pro-Ala 2:1. A simple change in residue order resulted in dramatic changes in thermal stability and properties. Characteristic Pro vibrations were observed at ∼75 °C higher temperature in Pro-Ala than Ala-Pro. The appearance/disappearance of characteristic vibrational modes with increasing temperature showed that a double peak in the Ala-Pro major phase transition (174–184 °C) was due to a gauche to anti 165° rotation of H₃CC*NH₃ about C*. CH₂ rocking and wagging frequencies present in Pro-Ala were not observed in Ala-Pro. For Ala-Pro, the Ala ⁺NH_3, and Pro COO⁻ sites were flexible whereas the Pro ring moiety was not; since the OCN (C)₂ amide bond is planar the CNC moiety keeps the Pro ring rigid. For Pro-Ala, CH₂ sites in the Pro ring were flexible and the OCNH amide bond is perpendicular to the Pro ring. Since the mass of the Pro ring is significantly larger than the mass of the flexible Ala ⁺NH₃ moiety, Pro-Ala absorbs more thermal energy, corresponding to a higher phase transition temperature (240–260 °C). Ala-Pro, Pro-Ala, and Ala-Pro/Pro-Ala 2:1 exhibited α-helix, β-sheet, α-helix secondary structure conformations, respectively.     

Mechanism of rhodium(III)-catalyzed formal C(sp3)H activation/spiroannulation of α-arylidene pyrazolones with alkynes: A computational study

DFT calculations were performed to investigate the rhodium-catalyzed formal C(sp³)-H activation/ spiroannulation of α-arylidene pyrazolones with alkynes. The calculations indicate that the spiroannulation through the proposed C-C reductive elimination is kinetically unfeasible. Instead, the C-C coupling from the eight-membered rhodacycle was proposed to account for the experimental results     

A theoretical study on the alkene insertion step in Rh-Yanphos catalyzed hydroformylation

This paper studied the mechanism of the alkene insertion elementary step in the asymmetric hydroformylation （AHF） catalyzed by RhH（CO）2[（R,S）-Yanphos] using four alkene substrates （CH2=CH- Ph, CH2=CH-Ph-（p）-Me, CH2=CH-C（==O）OCH3 and CH2=CH-OC（=O）-Ph, abbreviated as A1-A4）. Interestingly, the equatorial vertical coordination mode （A mode） with respect to the Rh center was found for AI and A2 but not for A3 and A4, although the equatorial in-plane coordination mode （E mode） was found for A1 -A4. The relative energy of the E mode of the -q2-intermediates is lower than that of the A mode. In the alkene insertion step, Path 1 is more favorable than Path 2 for this system. As for AI and A2, there could be a transformation between 2eq and 2ax.     

Nucleophilic substitution of 4-bromomethyltriazolium with different nucleophiles

1,2,3-Triazolium salts draw much attentions in recent years. We developed a new synthetic method to heteroatom-functionalized triazoliums via nucleophilic substitution of 4-bromomethyltriazolium. This method afforded triazoliums with different S, N, and O heteroatom-substituents. Moreover, S_N2′ reaction was observed with alcohols or hydroxides. In addition, debromination and debromomethylation reaction occurred in some cases.     

Copper-catalyzed NH/SH functionalization: A strategy for the synthesis of benzothiadiazine derivatives

A copper-mediated NS bond-forming reaction via NH/SH activation is described. This reaction occurs under mild conditions with high efficiency, step economy, and tolerates a wide variety of functional groups, providing an efficient means of accessing biologically important 1,2,4-benzothiadiazin-3(4H)-ones.     

Oxidation and reduction of nanodiamond particles in colloidal solutions by laser irradiation or radio-frequency plasma treatment

Functionalized nanodiamond particles (NDs) represent carbon nanomaterial with unique properties for various applications. Here we report on a new approach to surface modification of NDs by their exposure to radio frequency (RF) plasma or laser irradiation (LI) plasma directly in aqueous solution. By using grazing angle reflectance Fourier transform infrared spectroscopy and supporting analysis by X-ray photoelectron spectroscopy, zeta-potential, and Kelvin force microscopy we show that surface chemistry of NDs produced by detonation process (DNDs) or high-pressure high-temperature process (HPHT NDs) works in different way. Moieties on as-received NDs are dominated by COOH and COC groups due to wet chemical cleaning procedures. On DNDs, both RF and LA treatment lead to removal of sp² shell and additional oxidation of the surface to C OC groups. On HPHT NDs the RF treatment leads to reduction of COC groups that are transformed into COH and CH moieties. Thus at least partial hydrogenation of colloidal HPHT NDs seems feasible.     

Theoretical calculations of the substituent effect on molecular properties of the RCN⋯HF hydrogen-bonded complexes with R = NH2, CH3O,CH3, OH,SH, H,Cl, F,CF3, CN and NO2

DFT calculations with B3LYP and PBE1PBE functionals and 6–311++G(d,p) basis set have been performed in order to obtain molecular geometries, binding energies and vibrational properties of the RCN?HF H-bonded complexes with R = NH₂, CH₃O, CH₃, OH, SH, H, Cl, F, CF₃, CN and NO₂. As expected, it has been verified as a red-shift of the HF stretching frequency (ν_HF), in conformity with the elongation of the bond after complexation. On the other hand, the CN stretching frequency (ν_CN) is blue-shifted and corresponds to a shortening of the bond. The binding energies (ΔE_c), including BSSE and ZPVE corrections, show a linear correlation with several structural, electronic and vibrational properties. In particular, an important linear dependence between the binding energy and the calculated dipole moment of the free RCN molecule (μ_RCN) has been found. This result suggests that μ_RCN can be a useful quantity in order to predict the ability of this fragment to form a hydrogen-bond. The IR intensities of stretching and bending modes of complexed HF acid fragment are adequately interpreted through the atomic polar tensor of the hydrogen atom in HF using the modified CCFO model for infrared intensities. The new vibrational modes arising from complexation show several interesting features.     

The effects of hydrogen on KOH activation of petroleum coke

KOH activation of petroleum coke (PC) was conducted with 30 vol%H₂ + 70 vol% N₂ as carrier gas. TG-DTG, FTIR, elemental analysis, N₂ adsorption, GC and XRD techniques were used to investigate the effects of hydrogen on the activation. During the initial stage of the activation, i.e. the carbonization of the PC, additional CH and CH₂ species were formed due to the chemisorption of hydrogen on the nascent sites of the PC created by the removal of the surface heteroatom groups. The formation of the CH and CH₂ species increased the quantity of ‘active sites’ which is favorable to the further activation reaction, and developed the porous structure of the activated carbons. The micropore volume and BET surface areas of the activated carbon prepared under 30 vol% H₂ + 70 vol% N₂ and with a relatively low KOH/PC weight ratio of 2:1 have been increased from 0.78 cm³/g and 1936 m²/g to 0.97 cm³/g and 2477 m²/g, respectively, compared to that prepared in pure N₂ atmosphere with the same KOH/PC ratio.     

The Raman spectra of serine and 3,3-dideutero-serine in aqueous solution

The Raman spectra of serine [α-amino-β-hydroxypropionic acid; HOCH₂CH(NH₃)⁺COO⁻] and 3,3-dideutero-serine [HOCD₂CH(NH₃)⁺COO⁻] in aqueous solution were studied in the range 4000–300 cm⁻¹. The data obtained for the deuterated compound are novel and provide compelling evidence that previously reported assignments for the undeuterated amino acid should be revised.     

Structural,spectroscopic, and computational characterization of the cleavage product of dimolybdenum(II) core under aerobic conditions

Full characterization of the adduct isolated in crystalline form from a solution of tetrakis(μ-trifluoroacetato) dimolybdenum(II) and (2S,3S)-butane-2,3-diol is reported herein. For this purpose X-ray crystallographic, spectroscopic, and computational methods were conducted. The single crystal X-ray diffraction analysis clearly indicates the cleavage of the MoMo quadruple bond in the chiral complex initially formed in situ after mixing the components. Cleavage product 2 shows two coordinated, symmetrically unequivalent (2S,3S)-butane-2,3-diol ligands associated with one Mo atom with different MoO bond lengths and MoOC bond angles. This inequivalence most likely reflects the engagement of the coordinated butanediol ligands in an intermolecular hydrogen bonding interaction with solvating butanediol molecules leading to the formation of an infinite helical chain pattern. Density functional theory (DFT) and time-dependent DFT calculations were used to provide support for the proposed structural assignment of 2 in acetonitrile and chloroform solutions, which were made on the basis of experimental CD and NMR results. Additional studies under anaerobic conditions have shown that the cleavage of the quadruple MoMo bond takes place only under aerobic conditions. Thus, it has been demonstrated that the changes in the shapes of the ECD curves observed over time are associated with spontaneous, air-oxidative cleavage of the quadruple MoMo bond and conversion of the Mo(II) to Mo(VI) centers.     

Nitrogen- and oxygen-bridged bidentate phosphaalkene ligands

An overview is given on synthesis and structures of new bidentate phosphaalkene ligands [(RMe₂Si)₂CP]₂E (E = O, NR, N^?) and (RMe₂Si)₂CPN(R′)PR′′₂. Exceptional properties of these ligands, extending beyond predictable properties of phosphaalkenes are: (i) the NSi bond cleavage of [(iPrMe₂Si)₂CP]₂NSiMe₃ with Au^I and Rh^I chloro complexes under mild conditions leading to binuclear complexes of the 6π-delocalised imidobisphosphaalkene anion [(iPrMe₂Si)₂CP]₂N^?, and (ii) the chlorotropic formation of molecular 1:2 Pd^II and Pt^II metallochloroylid complexes with novel ylid-type ligands [(RMe₂Si)₂CP(Cl)N(R)PR₂]^?, and the transformation of a P-platina-P-chloroylid complex into a C-platina phosphaalkene by intramolecular chlorosilane elimination. Properties of the heavier congeners [(RMe₂Si)₂CP]₂E (E = S, Se, Te, PR, P^?, As^?) and (RMe₂Si)₂CPEPR′′₂ (E = S, Se, Te) are also described.     

CuLn complexes with a single μ-oximato bridge

Two original dinuclear (LnYb, 3 and LnEr, 4) and one trinuclear Cu^IILn^IIICu^II (LnGd, 5) complexes derived from a polydentate non symmetrical Schiff base ligand H₂L have been prepared. The ligand possesses two functions (phenol and oxime) able to coordinate the Ln ions, but structural studies (X-ray diffraction and powder X-ray diffraction) show that the Cu^II and Ln^III ions are only bridged by the oximato (NO) pair. The missing phenoxo bridge is replaced by a surprising pseudo-bridge involving one oxygen atom of the nitrato anion linked to the Cu and Ln ions according to a η²: η¹: μ mode. Although this latter contact has no role from the magnetic point of view, it introduces a large deformation of the unique bridging network. The CuYb complex 3 and the trinuclear CuGdCu complex 5 present antiferromagnetic interactions, with a J_CuGd interaction equal to ?1.25 cm^?1 in 5. The genuine single bridge can be considered as responsible for the antiferromagnetic character of the interaction.     

Structural properties of montmorillonite intercalated with tetraalkylammonium cations—Computational and experimental study

Several tetraalkylammonium (TAA) cations intercalated in layered clay mineral montmorillonite were studied by a combination of theoretical approach based on density functional theory (DFT) and infrared spectroscopy. DFT calculations revealed positions of TAA cations in the interlayer space and a dependence of d₀₀₁ parameter on the cation size. A finite difference method and molecular dynamic simulations were used to analyze and interpret vibrational modes observed in the experimental spectra with a specific focus on the CH₃ and CH₂ stretching modes. MD simulations on the tetraethylammonium-montmorillonite (TEA-M) model showed a high sensitivity of the position of the stretching vibrations of the CH₃ and CH₂ groups on the d₀₀₁ value. MD calculations also helped to distinguish vibrations of the parallel and perpendicular CH₃ groups of the tetramethylammonium-montmorillonite (TMA-M) which was not possible from the experimental infrared spectra because of many overlapping broad bands.     

Two-dimensional correlation infrared spectroscopy studies on the thermal-induced mesophase of 4-nitrobenzohydrazide derivative

Two-dimensional (2D) correlation infrared (IR) spectroscopy has been applied to explore the effect of hydrogen bondings (HBs) on the structure of mesophase in the dissymmetrical 4-nitrobenzohydrazide derivative, N-(4-cetyloxybenzoyl)-N′-(4′-nitrobenzoyl) hydrazine (C16-NO₂). The strength and species of HBs as well as the heat-induced structural variations in mesophase have been investigated. It has been found from 2D correlation IR spectroscopy that the sequential order of changes in the different functionalities in the course of liquid crystalline formation is that, firstly, the alkyl chain changes from the significant population of the trans conformation to the significant population of gauche conformation; then, the intermolecular HB between CO and NH groups is weakened, some even being broken, and consequently, the intermolecular distance is enlarged; finally, the skeleton of phenyl ring has enough space to change their conformation to weaken the π–π stacking interaction. In addition, besides a few free and some medium bonded NH and CO groups, strongly bonded NH and CO groups still predominantly exist in the mesophase.     

Transition-metal-catalyzed CH functionalization for late-stage modification of peptides and proteins

The present review surveyed the progress achieved in the late-stage modification of peptides and proteins utilizing transition- metal-catalyzed C-H functionalization with C-C and C-X (F, Cl, O, N, B, etc.) bonds formation.     

Dynamic behavior of polymer films in the presence of plasticizers by using ATR-based dynamic compression modulation step-scan Fourier transform infrared spectroscopy,and 2D correlation analysis

Attenuated total reflection (ATR)-based dynamic compression modulation two-dimensional (2D) correlation study of iso-phthalate based polyester (PES) films in the presence or absence of triphenyl phosphate (TPP) is carried out. In the PES without TPP, the dynamic response of side-chain (CO) groups is faster than that of the backbone (CCO) stretching, which is similar to the sequential result of our previous paper. With 15% TPP, the response of the backbone (CCO stretching) bands become faster than the side-chain (CO stretching) bands. In the case of 35% TPP, although slight differences are found, almost all of the observed peaks become synchronized with each other. The dynamic response feature is dramatically altered in the 45% TPP, suggesting that a transition point of larger molecular environment changes may exist between 35% and 45%. A model is proposed to explain these dynamic response features.     

Polymer brushes on hydrogen-terminated silicon substrates via stable Si—C bond

A universal and straightforward method for the preparation of polymer brushes via the formation of Si-C bond on silicon substrates through the UV-induced photopolymerization is demonstrated.     

Strong vibrational exciton coupling effects in polarized IR spectra of the hydrogen bond in 2-thiopyridone crystals

This paper presents the results of investigation on polarized IR spectra of the hydrogen bond in 2-thiopyridone crystals. The spectra were measured in the frequency range of the NH and ND bond stretching vibrations, for two different crystalline forms, having developed ab or bc crystal faces. The spectra exhibited extremely strong vibrational exciton coupling effects characterized by a large Davydov-splitting (correlation field splitting), whose existence was confirmed by a strong difference between the polarized spectra of the two forms of 2-thiopyridone crystals. It was shown that extremely strong exciton interactions involving the translationally non-equivalent hydrogen bonds in the unit cell are responsible for these effects. Isotopic dilution in the crystals caused the disappearance of the spectral effects, ascribed to the inter-dimer exciton couplings, and the simultaneous retaining of the dimeric character of the “residual” ν_NH and ν_ND bands. This spectral behavior of the isotopically diluted crystals was interpreted as the result of the dynamical co-operative interactions involving the hydrogen bonds in the lattice. These interactions lead to a non-random distribution of the protons and deuterons in the cyclic hydrogen bond dimeric systems and in consequence to the so-called H/D isotopic “self-organization” effects in the crystal spectra. The fine structure of the “residual” ν_NH and ν_ND bands is also influenced by such non-conventional spectral effects as the selection rule breaking for IR transitions, as well as the “reversal” exciton coupling effect for centrosymmetric hydrogen bonded dimers. This statement is supported by model calculations of the analyzed band shapes. They are performed in terms of the “strong-coupling” theory which assumes a strong anharmonic coupling involving different frequency hydrogen bond normal vibrations in the dimers, namely the high-frequency NH stretching and the low-frequency ν_N⋯S hydrogen bond stretching vibrations.     

Structural studies of bis(histidinato)nickel(II): Combined experimental and computational studies

A distorted octahedral nickel(II) complex, [Ni(2-amino-3-(1H-imidazol-4-yl)propanoic acid)₂] (1), has been synthesized by a solvothermal method and characterized by single-crystal X-ray diffraction. Geometry optimization in the gas phase and pyridine together with Hirshfeld surface and reduced density gradient analyses reveal that this complex shows different distortions from octahedral in the gas, liquid, and solid phases. The reason seems to be because of the presence of two intramolecular NH⋯O weak interactions in the gas phase and two sets of rather strong intermolecular NH⋯O and CH⋯O interactions in the solid phase. Time-dependent density functional theory (TD-DFT) calculations suggest that these different distortions result in different electronic absorption spectra.